In general, food is considered animal and vegetable, because it comes from animals and plants. But to know what food does for physical growth, energy, and health requires that one know more about foods than simply that they are animal and vegetable.

It is through study of food that one learns what food does for the body and how it does this; how cooking can aid in doing it; and how different kinds of food help the body differently. Starchy vegetables, such as potatoes, give it energy. What is known about what to eat, how to cook, what food does, needs to be considered together. It is thus one becomes able to choose and prepare foods that will keep a body well, help it to grow, and make it strong and full of energy.

It is customary to eat more than one food at a time and such foods together as taste and seem different, as bread and butter. Such foods have been found to be different and are called by different names, as meats, vegetables, fruits. The combination of foods generally eaten together is called a diet. It is from foods eaten together that the body gets the nourishment it needs for health, energy, and ability to grow.

It is therefore a diet, a food-combination, - foods eaten together, - which supports life and provides energy. The foods eaten together must therefore make a food-combination that will build the body, keep it in good running order, and supply it with energy.

To know what foods should be combined in order to do for the body what food can do, it is necessary to know what each food is and does. The composition of foods and the use of each to the body need therefore to be known in order to know how to combine foods to provide for growth, energy, health.